Compline is the last of the liturgical celebrations within the daily cycle of the Roman Catholic Divine Office. Intended for observance at the completion of the day, or prior to sleep, Compline is the office immediately following Vespers and, as with each of the hours of the Divine Office, contains a corpus of plainchant in the form of psalms, a hymn, antiphons, and smaller chants such as versicles, responsories, canticles, and others. This dissertation is primarily intended to serve as a resource for conductors and other musicians who are interested in exploring Compline in performance, whether in a liturgical or a concert setting. The document begins with an introductory chapter to establish the purpose and need for the study, as well as to define its parameters and to discuss related literature and potential future research. Chapter II provides an historical overview of the evolution of Compline from its origins in early Christianity to the Second Vatican Council in the twentieth century. Conductors who wish to integrate Compline plainchant with performances of related polyphonic settings will find in subsequent chapters original transcriptions in modern notation of all Compline plainchant from the Roman Breviary; original English translations of all Latin texts; an extensive catalog of polyphonic settings spanning all periods of music history; and a model concert program for a Compline-centered performance, complete with original performance editions of 12 Medieval and Renaissance polyphonic motets for various combinations of voices.